1. Field of the Invention
This disclosure relates to a self-lubricating ball bearing which is suitable for use especially in a high-speed application such as in a dental handpiece.
2. Description of the Related Art
A conventional bearing includes an outer raceway, an inner raceway and a retainer (also known as a cage or a separator) with balls placed between the outer raceway and the inner raceway. The retainer separates and positions the balls at approximately equal intervals around the bearing""s raceway. The retainer can be made from metallic or non-metallic materials. The non-metallic retainers are light weight, quiet, wear resistant and serve as an oil reservoir because of the material""s porous structure. Non-metallic retainers are particularly suitable for use in high-speed ball bearings.
U.S. Pat. No. 3,199,934 describes a conventional self-lubricating bearing having an outer raceway, an inner raceway and a metallic retainer. The retainer of the patent is formed of a composition containing silver, platinum, molybdenum disulfides, lead oxide and silicon dioxide such that the composition material itself acts as a solid lubricant.
U.S. Pat. No. 3,863,962 teaches a retainer made from polymeric material having a filler, such as a metallic sulfide, that has desirable lubricating properties. U.S. Pat. No. 5,988,891 teaches a retainer made from a melt-moldable fluororesin used with a raceway having an adhered to film of solid lubricant. U.S. Pat. No. 4,966,552 teaches the use of ceramic balls to reduce friction between the balls and other parts of the bearing. Conventional non-metallic retainers can be made from a polymer or phenolic material. The conventional polymer retainers can be made from, for example, polyamide, polyamideimides, polyetherethrketones, Vespel(trademark) or Meldin(trademark). However such retainers have limited grease and oil retaining properties due to insufficient porosity. On the other hand, conventional phenolic retainers have better porosity and therefore better lubrication retaining properties, but are not as strong mechanically as polymer retainers and break, for instance, upon being subjected to repetitive autoclave cycles.
None of the above mentioned patents teach the use of a solid lubricant in combination with another lubricant impregnated within the solid lubricant. Additionally, it is desirable to create a lubrication tolerant retainer with good mechanical properties for use in a ball bearing. It is also desirable to create a composite retainer from a strong polymer but with better lubrication retaining properties. Further, it is desirable to create a retainer which has a highly porous layer of solid lubricant capable of being impregnated with an additional lubricant.
The retainer of the present invention overcomes the aforesaid shortcomings of the prior art, while at the same time providing a wear resistant, mechanically strong retainer with a highly porous surface that is suitable for making lubrication tolerant bearings for use in dental handpieces and rotary tools.
The retainer of the present invention is made of a composite material having a body (or core) made from a polymer, and a layer of solid lubricant formed over the body by chemically coating the body with a porous layer of solid lubricant and impregnating the solid lubricant with another lubricant using a conventional method such as vacuum impregnation. The retainer is placed between an outer raceway and an inner raceway to form a self-lubricating bearing. The bearing made in this manner has high lubrication tolerance (i.e. it performs well in the absence of external lubrication). Because of its high lubrication tolerance, such a bearing is suitable for use in various applications such as dental/medical handpieces that are periodically sterilized, machine tool spindle motor applications which occasionally experience periods of lubrication starvation (such as at machine start-up), fan motors, DC motors, and stepping motors. It is also especially useful for any motor used in an environment hostile to a lubricant such as a vacuum environment or a high frequency occultation application in which lubricant is pushed off of the raceway surfaces by high frequency oscillation or high speed rotation.
Further features and advantages will appear more clearly on a reading of the detailed description, which is given below by way of example only and with reference to the accompanying drawings.